acdream/src/AcDream.Core/Physics/EntityCollisionFlags.cs

using AcDream.Core.Items;

namespace AcDream.Core.Physics;

/// <summary>
/// Per-entity flags driving the retail-faithful PvP / Player /
/// Impenetrable exemption logic in <c>FindObjCollisions</c>. Decoded
/// from <c>PublicWeenieDesc._bitfield</c> at <c>CreateObject</c> time.
///
/// <para>
/// Bit positions (verified against
/// <c>docs/research/named-retail/acclient_2013_pseudo_c.txt:406898-406918</c>
/// where <c>ACCWeenieObject::IsPK/IsPKLite/IsImpenetrable</c> read directly
/// from <c>this-&gt;pwd._bitfield</c>):
/// </para>
/// <list type="bullet">
///   <item><c>BF_PLAYER          = 0x8</c>        (bit 3)  → <see cref="IsPlayer"/></item>
///   <item><c>BF_PLAYER_KILLER   = 0x20</c>       (bit 5)  → <see cref="IsPK"/></item>
///   <item><c>BF_FREE_PKSTATUS   = 0x200000</c>   (bit 21) → <see cref="IsImpenetrable"/></item>
///   <item><c>BF_PKLITE_PKSTATUS = 0x2000000</c>  (bit 25) → <see cref="IsPKLite"/></item>
/// </list>
///
/// <para>
/// <see cref="IsCreature"/> is NOT a PWD bit — retail derives it from
/// <c>PublicWeenieDesc._type</c> matching <c>ITEM_TYPE_CREATURE</c>
/// (acclient.h ITEM_TYPE enum). Set at registration time by callers that
/// already know the item type.
/// </para>
/// </summary>
[Flags]
public enum EntityCollisionFlags : byte
{
    None           = 0x00,
    /// <summary>Set when <c>BF_PLAYER (0x8)</c> is set in <c>pwd._bitfield</c>.</summary>
    IsPlayer       = 0x01,
    /// <summary>Derived from <c>ItemType.Creature</c> on the spawn payload.</summary>
    IsCreature     = 0x02,
    /// <summary>Set when <c>BF_PLAYER_KILLER (0x20)</c> is set.</summary>
    IsPK           = 0x04,
    /// <summary>Set when <c>BF_PKLITE_PKSTATUS (0x2000000)</c> is set.</summary>
    IsPKLite       = 0x08,
    /// <summary>Set when <c>BF_FREE_PKSTATUS (0x200000)</c> is set (a.k.a. "Free" PK status — cannot be PKed).</summary>
    IsImpenetrable = 0x10,
    /// <summary>
    /// Runtime collision metadata: the target has a retail
    /// <c>CWeenieObject</c>. This is deliberately distinct from
    /// <see cref="IsCreature"/> because doors, portals, and items also have a
    /// weenie. <c>OBJECTINFO::missile_ignore</c> at <c>0x0050CEB0</c>
    /// requires this distinction for ethereal targets.
    /// </summary>
    HasWeenie      = 0x20,
    /// <summary>
    /// AP-71 (Campaign P Slice P4, 2026-07-30): set when BOTH
    /// <c>BF_ADMIN (0x100000)</c> and <c>BF_IMMUNE_CELL_RESTRICTIONS
    /// (0x400000)</c> are set in <c>pwd._bitfield</c> — the exact two-bit AND
    /// retail's <c>ACCWeenieObject::CanBypassMoveRestrictions</c>
    /// (0x0058c500) evaluates to let a mover through an access-restricted
    /// (house-barrier) cell without an owner/guest-list check. Bit names
    /// confirmed at <c>acclient.h:6452-6454</c>
    /// (<c>PublicWeenieDesc::BitfieldIndex</c>); <c>BF_ADMIN</c> is
    /// independently decoded the same way in
    /// <see cref="AcDream.Core.Ui.RadarBlipColors"/>.
    /// </summary>
    CanBypassMoveRestrictions = 0x40,
}

/// <summary>Helpers to convert raw retail bitfields into <see cref="EntityCollisionFlags"/>.</summary>
public static class EntityCollisionFlagsExt
{
    /// <summary>
    /// Decode the player/PK/PKLite/Impenetrable bits from a
    /// <c>PublicWeenieDesc._bitfield</c> value (the WeenieHeader trailer
    /// field acdream's parser surfaces as <c>ObjectDescriptionFlags</c>).
    ///
    /// <para>Bit positions per
    /// <c>docs/research/named-retail/acclient.h:6431-6463</c>
    /// (<c>PublicWeenieDesc::BitfieldIndex</c>) and
    /// <c>acclient_2013_pseudo_c.txt:441868-441890</c>
    /// (<c>PublicWeenieDesc::SetPlayerKillerStatus</c>).</para>
    /// </summary>
    public static EntityCollisionFlags FromPwdBitfield(uint bitfield)
    {
        var flags = EntityCollisionFlags.None;
        if ((bitfield & 0x8u)        != 0) flags |= EntityCollisionFlags.IsPlayer;
        if ((bitfield & 0x20u)       != 0) flags |= EntityCollisionFlags.IsPK;
        if ((bitfield & 0x200000u)   != 0) flags |= EntityCollisionFlags.IsImpenetrable;
        if ((bitfield & 0x2000000u)  != 0) flags |= EntityCollisionFlags.IsPKLite;
        // AP-71: BF_ADMIN (0x100000) AND BF_IMMUNE_CELL_RESTRICTIONS (0x400000),
        // matching CanBypassMoveRestrictions' own AND (not OR) of the two bits.
        if ((bitfield & 0x100000u) != 0 && (bitfield & 0x400000u) != 0)
            flags |= EntityCollisionFlags.CanBypassMoveRestrictions;
        return flags;
    }

    /// <summary>
    /// TS-23 (Campaign P Slice P3, 2026-07-30): translate the decoded
    /// per-entity <see cref="EntityCollisionFlags"/> (the PWD-bitfield
    /// bit-space) into the <see cref="ObjectInfoState"/> bits
    /// <c>CollisionExemption.ShouldSkip</c> and the moverFlags argument to
    /// <c>PhysicsEngine.ResolveWithTransition</c> actually consume — a
    /// DIFFERENT bit-space (retail <c>OBJECTINFO::init</c> 0x0050cf30
    /// `state |= 0x80/0x800/0x1000`, acclient.h:6190-6194) that must not be
    /// confused with the PWD wire numbering. <see cref="EntityCollisionFlags.IsPlayer"/>
    /// is deliberately NOT translated here — every existing mover-flags call
    /// site already derives <see cref="ObjectInfoState.IsPlayer"/> from its
    /// own GUID-prefix heuristic (correct per #184 Slice 2b) and this helper
    /// only fills the gap that heuristic cannot: PK/PKLite/Impenetrable.
    /// </summary>
    public static ObjectInfoState ToMoverState(this EntityCollisionFlags flags)
    {
        var state = ObjectInfoState.None;
        if ((flags & EntityCollisionFlags.IsPK) != 0) state |= ObjectInfoState.IsPK;
        if ((flags & EntityCollisionFlags.IsPKLite) != 0) state |= ObjectInfoState.IsPKLite;
        if ((flags & EntityCollisionFlags.IsImpenetrable) != 0) state |= ObjectInfoState.IsImpenetrable;
        // AP-71 (Campaign P Slice P4): the mover's own house-restriction bypass,
        // consumed by ObjectInfo.CheckEntryRestrictions.
        if ((flags & EntityCollisionFlags.CanBypassMoveRestrictions) != 0)
            state |= ObjectInfoState.CanBypassMoveRestrictions;
        return state;
    }

    /// <summary>
    /// TS-23 (Campaign P Slice P3, 2026-07-30): the one shared
    /// <c>ClientObjectTable</c>-backed mover-flags lookup every physics
    /// call site (local player world-entry, remote DR sweep + teleport,
    /// ordinary movers) uses — was inlined three times (App
    /// <c>GameWindow</c>/<c>LivePresentationComposition</c>/
    /// <c>RemoteTeleportController</c>) before being consolidated here.
    /// An entity with no row, or a row with no wire bitfield yet, resolves
    /// to <see cref="ObjectInfoState.None"/> — a no-op OR into moverFlags,
    /// bit-identical to every pre-P3 caller.
    /// </summary>
    public static ObjectInfoState ResolveMoverPvpState(this ClientObjectTable objects, uint serverGuid)
    {
        ArgumentNullException.ThrowIfNull(objects);
        return objects.Get(serverGuid)?.PublicWeenieBitfield is { } bitfield
            ? FromPwdBitfield(bitfield).ToMoverState()
            : ObjectInfoState.None;
    }
}